As used herein, shear refers to the sliding motion of particles relative to one another, and shear stress is the application of forces to particles resulting from said sliding motion. Total applied shear or total shear refers to the total shear applied to a sample of particles over the entire process of holding, processing, and mixing the sample of products.
Shear plays an important role in the processing of pharmaceutical blends and other powder samples, thereby effecting the performance of mixtures. It has been known that excessive amounts of shear applied to a powder sample for a significant amount of time decreases the hardness, increases capping, and decreases the dissolution of tablets formed from the powder sample. It is also known in the art that the intensity of total applied shear for direct compression cohesive blends, effects particle size and shape, the density, flowability and content uniformity of said powder, and the weight variability of tablets formed therefrom. Furthermore, it is also known that the total applied shear correlates to electrostatic charging of the powder sample, which is a safety hazard and interferes with the process of manufacturing tablets from a powder sample. However, these relationships are not easily quantified.
It would be advantageous to study the physical relationships between the shear applied to a powder sample and the properties of tablets formed therefrom. An understanding of these physical relationships could be used, for example, to advance the state of the art in tablet production. However, in spite of its significant impact, shear has not been studied systematically. Typically, varying amounts of shear have been applied (often unintentionally) in a blender and/or in a feed frame. In both of these environments, the granular flow of the powder sample is poorly understood and the intensity and uniformity of shear that is applied to the powder sample is unknown. As a result, the knowledge in the art relating to the effect shear has on tablets is typically qualitative at best. In this regard, it is further unknown in the art how the amount of shear applied to a powder sample can be controlled to produce tablets having desired properties.
What is needed in the art is technology that facilitates testing and evaluation of the relationship between the shear imparted to a powder sample and the properties of the tablets produced therefrom.